Plasma disappearance curves of radiolabeled bilirubin, sulfobromophthalein, indocyanine green and bile acids are obtained in normal volunteers and in patients with hepatic disease. Curves are analyzed by computer to calculate anion clearance (e.g. CBR (ml/min/kg); CBSP, etc.) and, in the case of bilirubin, daily bilirubin turnover (BRT (micromol/kg/day)). Data are further analyzed in terms of compartmental models to estimate hepatic uptake and conjugation rates, storage capacity, liver/plasma concentration gradients and other parameters of the hepatic organic anion transport mechanisms which are of interest both for physiologic studies and in the diagnostic classification of hepatic dysfunction. Micromodifications of the above techniques have been developed which permit analogous data to be obtained in small animals. In addition, a technique has been developed for the isolation, purification and radiolabeling of conjugates of bilirubin. Studies with these preparations have indicated an appreciable affinity of conjugated bilirubin for intrahepatic binding proteins, such as ligandin, resulting in the existence of a significant intrahepatic storage pool for conjugated bilirubin. These two observations will require a re-examination of current concepts of the nature of the hepatic excretion of conjugated bilirubin.